Dependence of physical properties on composition in a series of high load‐bearing polyurethane foams. Part II. Effects of variations in reactant ratios

Abstract

AbstractData and interpretations are presented on the effects of chemical variations on the physical properties, and in particular, the compression–deflection characteristics of a series of high load‐bearing, open‐celled, shock‐mitigating polyurethane foams. The load‐bearing capability of the foam is considered to be a function of density and intrinsic stiffness of the polymer. Polyol components of the formulations consisted of a poly (oxypropylene triol) of approximately 4000 molecular weight and ethylene glycol. The blowing agents were water and trimerized linseed fatty acids. A solution of polymethylene polyphenylisocyanate and tolylene diisocyanate comprised the isocyanate mixture. Stannous octoate and N‐ethylmorpholine were th̀e dual catalysts. Load‐bearing capability of the foam was raised by increasing the concentrations of the isocyanates, poly (oxypropylene triol), stannous octoate, and by employing higher ratios of polymethylene polyphenylisocyanate to tolylene diisocyanate. Decrease in compressive strength resulted from increasing the quantity of blowing agents and N‐ethylmorpholine. Increasing the quantity of ethylene glycol gave load‐bearing properties which increased to a maximum and then decreased. Chemical variations are analyzed in terms of their effects on the properties of the polymeric networks. These include crosslink density, number and distribution of hydrogen bonds, chain orientation and mobility, and relative selectivity of the various reactions. Effects on the overall bulk properties of the foam are discussed in terms of the chemical composition.